


The Union

by NonstopCreatorOfNonsense



Category: Undertale (Video Game)
Genre: Alternate Universe, Alternate Universe - Underlust (Undertale), Blushing, Boys Kissing, Children of Characters, Cooking, Domestic Fluff, Ecto-Tongue (Undertale), Engagement, Family, Family Fluff, Flirting, Fluff, French Kissing, Gentle Kissing, Gill Papyrus, Happy, Happy Ending, Implied Sexual Content, Kissing, Long-Term Relationship(s), M/M, Making Out, Marriage Proposal, Mates, Original Character(s), Originally Posted on Tumblr, Pet Names, Relationship(s), Surprises, Teasing, Underlust Papyrus (Undertale), Underlust Sans (Undertale), betta - Freeform, brief nudity, heart shaped eye lights, proposing with food
Language: English
Status: Completed
Published: 2020-10-23
Updated: 2020-10-23
Packaged: 2021-03-26 21:47:42
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,815
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/30112503
Author URL: https://archiveofourown.org/users/NonstopCreatorOfNonsense/pseuds/NonstopCreatorOfNonsense
Summary: Nep and Lust have been together for a while now, and they even share a daughter, but they still haven't officially tied the knot; Nep plans to change that, and things change as a result
Relationships: Lust Sans/Neptune Sans, Lust Sans/Original Character
Kudos: 1





	The Union

The lake dweller let out a deep sigh, standing up to slip his shorts on. He was exhausted, especially after everything that had happened last night. Images flickered in his mind of his adorable partner leaning over him, his hands in the bedding on either side of his head. Nep couldn’t help but smile softly, his cheekbones turning a faint shade of teal; His mate was so beautiful like that… With his face flushed purple, heart shaped eye lights, and those oh-so-perfect ivory bones. _He was gorgeous_. Even in his _sleep_ , Nep had thought he was gorgeous. _Nothing_ would be able to change that, either.

A pair of smaller arms wrapped around him from behind, fingertips gently tracing along his sternum, and he arched a single brow bone as he heard Lust yawn. Laying his head on Nep’s back, Lust’s voice was still laced with sleepiness as he murmured, “Morning, Angel Fish… Did you sleep ok?” Smiling to himself again, Nep hummed in confirmation, “Mmhm… Sure did, Shortcake. I don’t think I’ve slept that good for _a while_ , actually. What about you?” The shorter of the two smiled tiredly, “I’m glad you slept so good. I think I slept pretty good too last night.” Nep delicately took one of Lust’s hands and raised it to his face, murmuring, “Good… I’m glad to hear it.”

Pressing a soft kiss to the back of the other’s hand, he let his teeth linger for a moment before turning to face his still half asleep partner. Tilting his head and sighing, he continued to smile, gently cupping Lust’s face and leaning down to steal a quick kiss. As he pulled away, Lust whined, making a face, “Nuh uh, mister. If you’re gonna kiss me, it’s gotta be _longer_ than that.” Raising a single brow bone again and snorting in amusement, Nep mumbled a half hearted apology, his hand still on Lust’s face as he leaned down again, gently kissing him. As expected, Lust was happy to return the kiss, his cheekbones dusting a pretty shade of violet as he pressed closer to Nep. Feeling the tip of Lust’s tongue trace over his teeth, Nep pulled away from the kiss, his grin widening as he took a playful tone, “Babe… What was _that?”_ The smaller of the two shrugged, clearly still tired yet, “What do you mean?” The lake dweller hummed, “I felt your tongue on my teeth. Just _what_ are you tryna do, short stuff?”

Lust cuddled up to Nep, content as the taller wrapped his arms around him, _“Maybe_ I wanted to make out with you a little.” Nep laughed softly, his cheekbones turning a light shade of teal, “Lust, Sweetheart… Baby doll. You _literally_ just woke up. If you wanna make out, we can do that later. ‘Sides, we have some stuff to do today anyway.” Lust let out a tired, exaggerated sigh, “ _Fiiiiiine_. What are we doing today though? You didn’t tell me we had plans.” The taller skeleton made a soft sound of acknowledgement, “ _Yeeeeah_ , I know I didn’t. It’s a surprise though, I didn’t wanna ruin it for ya.” Lust smiled tiredly, “Awe… Well look at you, being Mr. Romantic.” Nep playfully scoffed, his tone clearly teasing, “Me, romantic? _Pffft_. In case you’ve forgotten, I’m _still_ a human eater. A _cold, soulless being_ like me has no _idea_ what romance even is.” Arching a brow bone, Lust hummed, an amused look on his face, “Uh huh, sure. For someone who’s apparently cold and soulless, you sure do _love it_ when I scratch the underside of your jaw. I had you purring last night when I did that, remember? And you were so _cute_ , too.”

Nep felt a rush of heat to his face and he flicked his tongue at his partner, only causing the shorter of the two to laugh softly. Lightly nudging Lust back toward the bed, the lake dweller made a face, “Yeah yeah, sure, whatever. How about you get dressed now so we can start the day?” Lust took a step backward, shamelessly stretching his arms above his head, “What? I thought you liked seeing me naked like this.” Nep groaned, trying not to let his gaze wander over the other’s body, “God, yes, I do. Ya _damn well know it_ , Sweetheart. You gotta put some clothes on, or I have a feelin’ we’ll be down here for a while yet. You don’t want my bro comin’ down here and seeing you like this, do ya?” Immediately noticing Nep attempting not to let his eyes wander, Lust smiled and hummed softly, “No, I suppose not. That’d be pretty awkward, in all honesty.” The lake dweller made a sound of agreement, “My point exactly.” Lust began to gather his clothes, shooting a final glance at his partner before beginning to get dressed. It wasn’t long before both skeletons were ready to head out, making their way to the bunker’s exit. As if he was trying to show off, Nep was quick to open the ridiculously heavy looking door by himself, holding it in place as Lust slipped past him. Once Lust was out of the way, he released the door and pushed it shut, re-implementing some of his magic to act as a lock.

They found their way back to the lake where Nep usually stayed, and after a short pause and some discussion, they agreed on returning to Lust’s home to have their lunch. Which, from Nep’s perspective, was perfect. Crossing into Underlust and trudging through the snow toward the smaller skeleton’s house, Nep stole a glance down at their hands, gently clasped with their fingers intertwined as they walked. His cheekbones became a faint shade of teal and he glanced at Lust’s face, unable to keep himself from smiling sheepishly; Now, all he could do was hope and pray that everything went according to plan. As they stepped up onto Lust’s doorstep, Nep slipped his hand out of his mate’s grasp, instead opting to loop his arm around his waist, tugging him flush against his side. Lust let out a soft sound, clearly a bit surprised, and the taller monster offered a soft apology, pressing a kiss to the top of his skull. Of course, he was forgiven. All Lust asked for was a kiss before they went inside. They shared a quick kiss before slipping into the warm, well lit home, which smelled of fresh bread. In response to the smell, Nep heard his stomach grumble, and his cheekbones dusted teal again as Lust cast a glance up at him and chuckled, having heard the sound. On the couch, Betta was curled up with a pillow, lightly leaning against Gill. Surprised to see the younger brother of his mate present, Lust cleared his throat, politely greeting the monster in question as they emerged into the living room.

Gill happily returned the greeting, and had it not been for Betta murmuring something to him, he appeared as though he would’ve leapt off the sofa to capture his elder brother and Lust in a bear hug. Nep excused himself, heading off to the kitchen where he knew Charm could be found. Stepping past the kitchen threshold, Nep cleared his throat, “Hey buddy, we finally made it.” Looking up from the pot of chili that sat on the stovetop before him, Charm offered the lake dweller a polite smile, “HELLO, NEPTUNE. IT’S GOOD TO SEE YOU AGAIN.” Nep smiled sheepishly, glancing around the kitchen, “Yeah, you too. So… How’s this gonna work out? Are we eating and then doin’ the thing after, or?…” The UnderLust skeleton shrugged his shoulders, amusement flickering in his sockets, “WE CAN DO WHATEVER WORKS BEST FOR YOU. I KNOW THAT TO YOU AND YOUR BROTHER, THE OFFERING OF FOOD HOLDS A DIFFERENT MEANING THAN IT DOES TO MY BROTHER AND MYSELF. I… WOULDN’T WANT TO IMPOSE ON YOU OR SPOIL ANYTHING, SO IT’S YOUR CALL.”

Nep let out a deep sigh, his cheekbones gaining a soft teal blush again as he smiled slightly, “Thanks, Charm… The consideration means a lot. Seriously. It’s just… I don’t think I’ve _ever_ been this nervous in my life before, and I dunno what I should do.” The taller of the two checked his pot of chili a final time before switching off the stove, sighing as he approached the lake dweller and placed a hand on his shoulder, “I UNDERSTAND, MY FRIEND. IS THERE ANYTHING I CAN DO TO HELP CALM YOUR NERVES?” Nep was silent for a moment in thought before shaking his head, his voice softer than before, “I dunno… I guess I… What if he won’t accept it? What if he says _no?”_ Charm offered the shorter monster a gentle smile, lowering his voice, “Don’t Worry So Much About That, Neptune. I’m Sure He’ll Accept It. He’s My Brother, And Seeing As I Know Him So Well, I Know How Much He _Loves_ You. It’s Clear Every Time You’re Together, And He’s Always Talking About You Whenever He’s Chatting With One Of His Gossip Friends.” His blush darkened slightly further upon hearing Charm’s words, and he nodded sheepishly, momentarily closing his sockets. Opening them again and releasing a deep sigh, he looked up at this AUs Papyrus, smiling nervously, “Thanks, buddy… That means a lot. I uh… Did you leave the container where I left it yesterday?” The skeleton in question eagerly nodded, smiling brightly, “OF COURSE I DID! I TAKE IT WE’RE DOING THAT FIRST, THEN EATING AFTER?”

Humming in confirmation, the lake dweller slipped past him and knelt on laminated floor, opening a cupboard, “Yep. Hopefully I don’t chicken out or anything now.” As he began to dig through the cupboard, Charm playfully scoffed and waved off his words, “ _YOU_ , CHICKENING OUT? I _HIGHLY DOUBT_ YOU’D DO SUCH A THING.” Nep laughed softly, tugging out a plastic container after a moment, “Yeah, yeah… That’s a dumb thought, isn’t it?” Charm made a sound of agreement, taking a step back as Nep stood, nudging the cupboard door shut with his foot and setting the container on the counter. Opening it just enough to slip his hand in and withdraw the slightly dried and hardened piece of bread used to keep his offering fresh overnight, he looked everything over, and then tossed the bread in the nearby trashcan. He was still for a moment, before opening the container and completely removing the lid, setting it on the counter and revealing a batch of cookies. Lifting the container, he held it close to himself, his still flushed face becoming a slightly brighter shade of teal as he smiled sheepishly at Charm, “Oh boy, here we go… Wish me luck, pal.” Charm offered him a reassuring smile accompanied by two thumbs up, and Nep began to slowly head for the open doorway, letting out a deep, almost shaky sigh.

Exiting the kitchen, he made a beeline for the living room, momentarily pausing in the doorway upon seeing that his mate was nowhere in sight. Meeting his gaze, Betta tilted her head and smiled, wordlessly nodding toward the stairs. Easily understanding what she was telling him, he offered her a grateful smile in return, changing his course and now proceeding to make his way to the staircase. He ascended them in silence, wandering down the hall until he was just outside Lust’s bedroom. Shifting the container of cookies with one hand and hiding them behind his back, he drew in a deep breath, releasing it as an equally deep exhale, before raising his free hand to lightly knock on the closed door. Only a few seconds passed in silence before he could hear Lust calling out from the other side of the door, “Yeah?” Nep began to fidget, unable to stand still, “Hey Shortcake, it’s me… Can I come in?” Lust’s voice gained a light, cheerful tone as he replied, “Mmhm, you can come in if you want. You don’t even have to knock, you dork.” Nep smiled slightly and chuckled, grasping and twisting the doorknob before gently nudging open the door.

Slipping inside and nudging it shut behind himself, he tightened his grip on the container that remained hidden behind his back, his blush immediately darkening as he was greeted by the sight of his mate. Lust stood beside his bed, now wearing a clean pair of skinny jeans and a baggy tank top, some of his bones appearing slightly damp while droplets of water dripped from others. Ah, so he must’ve had a quick shower. Looking up as Nep slowly approached him, a smile settled on Lust’s face and he playfully arched a single brow bone, his tone teasing, “What are you hiding behind your back, mister? Is it part of the surprise you brought up this morning?” The taller of the two nodded sheepishly, his cheekbones still stained a deep shade of teal as he smiled slightly, “Well… _Yeah_ , you could say that.” With a brow bone still arched, Lust hummed softly, “May I see what it is?… I’m assuming that’s why you brought it in here, at least.” Nep fidgeted again, his blush visibly darkening as he slipped the container of cookies out from behind himself, holding it out and offering it to Lust. The shorter monster blinked in surprise, his cheekbones gaining a soft violet blush. He was quiet for a moment before speaking again, “Did you make these, Neptune?… By yourself?”

The lake dweller nodded, sheepishly glancing away and mumbling, “Uh huh… I did.” Lust fell silent again, and Nep began to worry, his gaze almost pleading as he watched his mate. Recalling what he’d been told by Betta and Gill, Lust felt heat rush to his face, his soft blush darkening before Nep’s eyes. Understanding what was happening, Lust smiled shyly, reaching out to accept the offering, taking a cookie from the container. Watching as Lust took a bite of the cookie, Nep’s sockets widened in shock, teal tears threatening to drip down his cheekbones. Setting the container on Lust’s bed, he wrapped his arms around his partner, holding him close and letting out a shaky sigh of relief as a smile began to slowly stretch across his face.

Though still just as embarrassed and shy as before, Lust finished the bit of cookie in his mouth and then lifted what was left of it, offering it to Nep. Despite the purr that began to rumble somewhere within his chest, he opened his mouth, being careful not to accidentally graze Lust’s fingers as he took a bite of the cookie. They continued to share the goodie until it was gone and Lust retrieved another, happily sharing it with the lake dweller just as they’d done before. Nep hummed softly, mindful of the container's location as he backed his mate up against the edge of his bed. He allowed Lust to finish what was left of his cookie, before proceeding to gently push him down onto his back on the bed, leaning over him and kissing him deeply. Happily returning the kiss, Lust smiled into it, a purple tear rolling down his face as he parted his teeth, allowing Nep to slip his ecto tongue into his mouth. Their tongues met and danced to some unheard rhythm, twisting and curling together, never losing contact.

As the lake dweller slowly pulled away, he began to purr just as loudly as before, gently nuzzling Lust’s cheekbone and pressing a soft kiss to his temple, murmuring to him, “God… You make me really happy, y'know that? So, _so_ fuckin’ happy.” Lust laughed softly, delicately cupping Nep’s face, “And You make me happy too, Neptune. _Really.”_ Nep leaned into his touch, briefly closing his sockets and simply breathing in his mate’s scent. Lust’s eye lights flickered, becoming small hearts as he gazed up at his partner in adoration, his soul swelling with joy. A moment passed before Nep sighed, pulling away from Lust and standing up. Lust sat up, his face stained with his purple blush still as he continued smiling, letting out a soft squeak in surprise as he was scooped up into Nep’s arms, instinctively wrapping his arms around his taller partner’s neck vertebrae. Grinning to himself as he carried his mate toward the door, Nep’s face gained an even brighter teal blush, a single tear rolling down his cheek. Reaching up to gently wipe away the tear, Lust smiled softly as Nep turned his head, gently kissing his hand.

Now all that was left to do was to share the good news.... The news that very soon, they would be married. Nep could hardly believe it; When he was cursed and turned into what he was now, the deity had told him he’d be horrifying, and essentially unlovable. _Maybe_ he was still horrifying sometimes, but if there was one thing he _wasn’t_ , it would be unlovable.

**Author's Note:**

> I borrowed one of Venelona's Horrortale headcanons for part of this (the bit with Nep offering Lust the cookies), since Nep's mentality and behavior is pretty similar to HT Sans'  
> To explain the headcanon, it's that when you offer someone food that you yourself made, that's considered a marriage proposal. If it's accepted (eaten), then yay, you're getting married!


End file.
